Thanks to continuing performance and yield improvements, increasing speeds, and higher pixel resolutions, liquid crystal (LC) spatial light modulator devices hold out considerable promise for expanded use in a range of display and projection apparatus. In spite of their growing acceptance, however, both thin-film transmissive LC display panels and miniaturized liquid crystal on silicon (LCOS) devices often exhibit luminance non-uniformity, particularly when the system is set to its darkest levels. This non-uniformity in luminance can be particularly perceptible toward the edges and corners of the display field and is often accompanied by undesirable shifts in tint and shading, particularly with an image having low luminance values. Luminance non-uniformity between display pixels also varies over the range of luminance values. That is, different non-uniformity effects such as non-monotonic response may or may not appear depending on whether a pixel is intended to be black, or within a relatively dark range, or elsewhere on the luminance scale. As yet a further complication, the relative chromaticity of pixels may vary with their luminance level. Thus, differences in luminance may adversely impact color fidelity as well.
There appear to be a number of possible causes for this luminance non-uniformity. Among sources of this performance problem are imperfections in the components of the optical path, including imperfections within the LCD itself, and thermal effects acting on the components. Because of its pervasive nature and complex combination of causes, this luminance non-uniformity problem has not yet been adequately addressed in many display apparatus designs. Instead, many display designers and vendors simply take it as a “given” that such luminance non-uniformity is to be expected with these devices.
Thus, it can be seen that there is a need for LC display apparatus with improved luminance uniformity and methods for achieving better uniformity when using liquid crystal spatial light modulators.